Your latest divert time is whatever you want it to be.
In other words whatever you are comfortable with so that you do not land with less than the required fuel minimums as dictated by either your company or the CAO requirements.
Bust the CAO minimum fuel requirement and watch both the law as well as your employer come down on you unless you have overriding circumstances.
After all, operational control does rest with the pilot in command unless security issues are involved etc etc etc.